Method of performing additive lookahead for adaptive cutting feedrate control

Abstract

The present invention relates to navigation of a path by a moving object, and, more particularly, to motion control systems for computer-controllable machine tools.

1. A method of computing velocity limitations for a plurality of motion commands provided to a motion controller to cause an object to move along a trajectory, including the steps of:
 providing a look-ahead queue including a plurality of motion commands, the plurality of motion commands including a first motion command; 
 calculating a first stop distance for the first motion command, the first stop distance being a distance between a first target point and a first virtual point beyond the first target point; 
 adding a second motion command to the plurality of motion commands in the look-ahead queue; 
 calculating a second stop distance for the second motion command, the second stop distance being a distance between a second target point and a second virtual point beyond the second target point; 
 using a computing device to modify a velocity limitation for the first motion command by reducing the first stop distance based on the second stop distance; and 
 providing the first motion command to the motion controller. 
 
   
   
     2. The method of  claim 1 , wherein the step of modifying a velocity limitation, includes the steps of:
 calculating a sum of a length of a motion segment associated with the second motion command and the second stop distance; and 
 comparing the first stop distance to the sum. 
 
   
   
     3. The method of  claim 2 , wherein the first stop distance is reduced if the first stop distance exceeds the sum. 
   
   
     4. The method of  claim 3 , wherein the first stop distance is reduced to equal the sum. 
   
   
     5. The method of  claim 1 , further comprising the steps of:
 adding a third motion command to the look-ahead queue; 
 calculating a third stop distance associated with the third motion command; and 
 determining if the second stop distance associated with the second motion command should be reduced based on the third stop distance, thereby modifying a velocity limitation for the second motion command. 
 
   
   
     6. A method of computing velocity limitations of motion segments having corresponding motion commands used by a motion controller for movement of a body along a trajectory, the motion segments including a first point having a first velocity and a target point having a target velocity, including the step of
 using a computing device to determine a virtual point beyond the target point having an end velocity, the virtual point being determined such that the trajectory includes the first point with the first velocity, the target point with the target velocity, and the virtual point with the end velocity, wherein the target velocity is greater than the end velocity and the first velocity is greater than the target velocity. 
 
   
   
     7. The method of  claim 6 , wherein the end velocity is zero. 
   
   
     8. The method of  claim 6 , wherein the trajectory is an S-curve velocity profile. 
   
   
     9. The method of  claim 6 , wherein the body passes through a plurality of positions between the first point and the target point and the trajectory has a unique speed value for each position of the body from the first point to the target point. 
   
   
     10. The method of  claim 6 , further including the step of determining a first distance between the target point and the virtual point. 
   
   
     11. The method of  claim 6 , wherein the motion segments further include a third point having a third velocity. 
   
   
     12. The method of  claim 11 , further including the steps of determining a second virtual point having a second end velocity, the second virtual point being determined such that the trajectory includes the target point with the target velocity, the third point with the third velocity, and the second virtual point with the second end velocity. 
   
   
     13. The method of  claim 12 , further including the steps of determining a first distance between the target point and the virtual point, determining a second distance between the third point and the second virtual point, and determining whether the first distance is sufficient to permit a change from the first velocity at the first point to the target velocity at the target point. 
   
   
     14. The method of  claim 13 , wherein the first distance is determined to be sufficient to permit the change from the first velocity at the first point to the target velocity at the target point if the first distance is less than or equal to the sum of the second distance and a length from the target point to the third point. 
   
   
     15. The method of  claim 13 , wherein if the first distance is greater than the sum of the second distance and a length from the target point to the third point, the first distance is determined to be insufficient to permit the change from the first velocity at the first point to the target velocity at the target point. 
   
   
     16. The method of  claim 15 , wherein if the first distance is greater than the sum of the second distance and a length from the target point to the third point, the first distance is reduced to a distance sufficient to permit the change from the first velocity at the first point to the target velocity at the target point. 
   
   
     17. The method of  claim 16 , wherein if the first distance is greater than the sum of the second distance and a length from the target point to the third point, the first distance is reduced to be equal to the sum. 
   
   
     18. The method of  claim 6 , wherein the body is a cutting head of a CNC machine. 
   
   
     19. The method of  claim 6 , further including the step of:
 providing motion commands to the motion controller for controlling a current velocity of the body along the trajectory, the providing step including the steps of 
 comparing at least two of a specified velocity; a machine allowable velocity; and a path velocity limit; and 
 setting the current velocity to a value not exceeding the lowest of the at least two of the specified velocity; the machine allowable velocity; and the path velocity limit. 
 
   
   
     20. The method of  claim 19 , wherein the current velocity at the target point does not exceed a joint velocity limit. 
   
   
     21. A method of computing velocity limitations for movement of a body along a contour having a plurality of segments, including the steps of
 sequentially storing in a queue a stop distance and a length associated with each segment, the stop distance being a distance between a target point and a virtual point beyond the target point; and 
 if a current stop distance associated with a current segment is greater than a sum of a subsequent stop distance and a subsequent length associated with a subsequent segment, then using a computing device to set the current stop distance equal to the sum and to verify that a prior stop distance associated with a prior segment is less than or equal to the current stop distance plus a current length associated with the current segment. 
 
   
   
     22. The method of  claim 21 , further including the step of
 recursively checking whether each stop distance is less than or equal to a subsequent sum of a stop distance and a length associated with a subsequent segment and reducing any stop distance in the queue that is greater than the subsequent sum; and 
 stopping the recursively checking step upon encountering a stop distance that is less than or equal to the sum of the stop distance and the length associated with the subsequent segment.